1. Field of Invention
The invention relates to lens grinding apparatus particularly for grinding concave surfaces of toric lens blanks with infinitely variable primary and secondary radii.
2. Description of the Prior Art
It has been the practice to grind concave surfaces on lens blanks to various predetermined degrees of curvature in a manner and with apparatus similar in some respects to that disclosed by the Applicant. However, the apparatus of the prior art differs from the Applicant's in that a grinding wheel of fixed diameter rotating about a horizontal axis is adapted to be pivoted about a vertical axis and positioned at various grinding angles relative to a radial plane passing through the lenses and the vertical axis or center about which the lens blanks move concentrically across the periphery of the grinding wheel. As a result, the grinding wheel situated at an angle grinds a concave surface having an elliptical (or parabolic) shape having non-concentric curvature of constantly changing radius in one direction or plane and a concentric curvature of constant radius in another direction or plane at right angles thereto. Also, a great number of interchangeable grinding wheels of various predetermined diameters must be kept on hand to grind lens blanks to the infinite number of different curvatures required at the present time.
The Applicant's invention provides apparatus which can grind concave surfaces to many different degrees of curvature and in which the curvatures in both directions are of constant radius. Additionally, the Applicant provides a grinding wheel movable in a single plane and whose diameter can be changed to grind a large number of different curvatures of constant radius on lens blanks without pivoting the wheel and changing the rotational grinding plane of the wheel.
Applicant is aware of the various radially expandable segmental grinding wheels of the prior art disclosed in the following U.S. Pat. Nos. 2,799,979 and 2,767,523. Unlike the Applicant's wheel, they require a greater number of separate elements and precision linkage or camming mechanism to shift individual abrasive segments between clamping flanges which must be released prior to making a radial adjustment. Applicant's segmental grinding wheel has abrasive segments fixed to angularly spaced peripheral surface portions of a slotted support center with integral deformable wall portions of relatively thin flexible and resilient material between radial slots about a hub portion. The shape of each of the deformable wall portions can be simultaneously varied by axially movable clamping flanges engaging opposite sides of the support center to change the diameter and radius of the wheel.